Send Orders of Reprints at [email protected] The Open Civil Engineering Journal, 2012, 6, (Suppl 1-M2) 121-130 121 1874-1495/12 2012 Bentham Open Open Access Fragility Analysis of Existing Unreinforced Masonry Buildings through a Numerical-based Methodology Amin Karbassi * and Pierino Lestuzzi Applied Computing and Mechanics Laboratory, École Polytechnique Fédérale de Lausanne, Station 18, 1015 Lausanne, Switzerland Abstract: As an approach to the problem of seismic vulnerability evaluation of existing buildings using the predicted vul- nerability method, numerical models can be applied to define fragility curves of typical buildings which represent building classes. These curves can be then combined with the seismic hazard to calculate the seismic risk for a building class (or individual buildings). For some buildings types, mainly the unreinforced masonry structures, such fragility analysis is complicated and time consuming if a Finite Element-based method is used. The FEM model has to represent the structural geometry and relationships between different structural elements through element connectivity. Moreover, the FEM can face major challenges to represent large displacements and separations for progressive collapse simulations. Therefore, the Applied Element Method which combines the advantages of FEM with that of the Discrete Element Method in terms of accurately modelling a deformable continuum of discrete materials is used in this paper to perform the fragility analysis for unreinforced masonry buildings. To this end, a series of nonlinear dynamic analyses using the AEM has been per- formed for two unreinforced masonry buildings (a 6-storey stone masonry and a 4-storey brick masonry) using more than 50 ground motion records. Both in-plane and out-of-plane failure have been considered in the damage analysis. The dis- tribution of the structural responses and inter-storey drifts are used to develop spectral-based fragility curves for the five European Macroseismic Scale damage grades. Keywords: Seismic Vulnerability Assessment, Applied Element Method, Fragility Analysis, Unreinforced Masonry. INTRODUCTION For regions where little damage data exist, small scale experimental tests and numerical modelling methods are good substitutes for the observed damage procedures in the process of the seismic vulnerability evaluation for existing buildings such as unreinforced masonry buildings. Experi- mental tests for even scaled buildings can be expensive and require special equipments, and are mainly performed on individual masonry walls instead [1,2]. On the other hand, different numerical methodologies from simple numerical procedures (e.g. [3,4]) to more complex dynamic methods (e.g., [5,6]) are conducted to study the seismic vulnerability of existing buildings. Simple procedures have also been pro- posed to study the nonlinear dynamic behavior of masonry building [7]. However, in the interest of achieving a simpler model for dynamic analysis, the model developed is based on two-dimensional behavior only. Nonetheless, many build- ings have irregular layouts that can result in a structure that behaves in complex three-dimensional ways under seismic loadings. Therefore, three-dimensional analysis should pro- duce a more accurate description of the behavior of the struc- ture during an earthquake. *Address correspondence to this author at the Applied Computing and Me- chanics Laboratory, École Polytechnique Fédérale de Lausanne, Station 18, 1015 Lausanne, Switzerland; Tel: +41 21 6936382; Fax: +41 21 6934748; E-mail: [email protected] This paper deals with the structural analysis of the ma- sonry building which faces several challenges due to the progressive collapse of masonry during an earthquake. To overcome these challenges, an alternative modelling tech- nique to the FEM is used here in combination with nonlinear dynamic analysis to consider both in- and out-of-plane be- havior for masonry buildings and to include the dynamic properties in the seismic vulnerability study. The objective of this paper is to present a numerical-based methodology to develop fragility curves for unreinforced masonry buildings. Those fragility curves can be used in combination with the hazard data of a region to perform a complete seismic risk assessment for the studied buildings. Such risk analysis [8], however, is out of the scope of this paper. MATERIALS AND METHODOLOGY Progressive Collapse in Masonry Structures In-plane damage mechanisms for masonry walls are gov- erned by failure modes in flexure (rocking), shear sliding along the joints, or shear diagonal cracking [9]. The occur- rence of each of those failure modes depends on several pa- rameters such as the wall boundary conditions, the axial load of the wall, masonry geometrical characteristics and con- stituents. Several references discuss the tendency of the prevalence of each failure mode based on the condition/value of those parameters (e.g., [10, 11]). It should be noted that there is not always a crystal clear certainty of the occurrence of a specific failure mode because many interactions may
Fragility Analysis of Existing Unreinforced Masonry Buildings through a Numerical-based Methodology
May 23, 2023
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